Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session B14: Mini-Symposium: Neutron-star mergers and the astrophysical r processFocus
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Sponsoring Units: DNP Chair: Artemis Spyrou, Michigan State University Room: Sheraton Plaza Court 3 |
Saturday, April 13, 2019 10:45AM - 11:21AM |
B14.00001: Nuclear physics and the GW170817 kilonova Invited Speaker: Rebecca A Surman Over a year ago we celebrated the incredible discovery of a neutron star merger event - GW170817 - in both gravitational and electromagnetic waves. The optical signal that accompanied GW170817 provided the first firm proof that neutron star mergers produce heavy elements. Still, it is not known exactly which elements are produced by mergers and in what proportions. Are neutron star mergers the sole astrophysical source of the heaviest elements via r-process nucleosynthesis or do other extreme events contribute? A full understanding of neutron star mergers and their role in galactic chemical evolution requires progress in a number of areas. One key area is nuclear physics. Thousands of exotic nuclear species participate in the r-process, and their properties shape abundance patterns and kilonova signals. Here we discuss how nuclear physics uncertainties influence predictions of neutron star merger nucleosynthesis observables. We will then explore the promise of experimental campaigns at rare isotope beam facilities to both reduce these uncertainties and provide insight into astrophysical environments of heavy element production. |
Saturday, April 13, 2019 11:21AM - 11:33AM |
B14.00002: FRLDM fission properties for the nucleosynthesis occurring in neutron star mergers Matthew R Mumpower August 2017 marked the first observation of gravitational waves and electromagnetic signals from the merging of two neutron stars sending ripples through the astrophysics, atomic physics, nuclear physics and gravitational wave communities. In some components of neutron star merger ejecta, fission is thought to re-cycle the material and impact the resultant abundances. I will discuss the fission properties that arise from the Finite-Range Liquid-Drop Model (FRLDM) covering the treatment of neutron-induced fission, beta-delayed fission and fission yields. The production of the heavy actinide Californium-254 in mergers will also be discussed. |
Saturday, April 13, 2019 11:33AM - 11:45AM |
B14.00003: The University of Notre Dame Multi-Reflection Time-of-Flight mass spectrometer for the N = 126 beam factory Maxime Brodeur, James M Kelly, Biying Liu The production of exotic nuclei at the vicinity of the N = 126 peak of the rapid-neutron capture process as for a long time pose a challenge. A new facility currently under construction at Argonne National Laboratory aims at undertaking the challenge by producing these difficult nuclei via multi-nucleon transfers reactions. The facility will first include a large-volume gas cell to collect and thermalize the reaction products. Then, upon extraction from the gas cell and radio-frequency ion guide, the ion beam will be separated by a high-resolution mass separator magnet and a multi-reflection time-of-flight mass spectrometer (MR-ToF) for the removal of isobaric contamination. This MR-ToF has been built and commissioned in an offline test setup at the University of Notre Dame. The commissioning results and off-line performance of the MR-ToF will be presented. |
Saturday, April 13, 2019 11:45AM - 11:57AM |
B14.00004: Beta-decay measurement for the A=130 r-process abundance peak Alfredo Estrade, Oscal Hall, Jiajian Liu, Giuseppe Lorusso, Fernando Montes, Vi Phong, Thomas Davinson, Keishi Matsui, Neerajan Nepal, Shunji Nishimura, Jorge Agramunt, Alejandro Algora, Nathan T Brewer, Roger Caballero-Folch, Francisco Calvino, Iris Dillmann, Cesar Domingo-Pardo, Robert K. Grzywacz, Gabor Kiss, Bertis C Rasco, Krzysztof Piotr Rykaczewski, Jose Luis Tain, Ariel Tarifeño-Saldivia, Alvaro Tolosa-Delgado, Phil Woods A new generation of radioactive ion beam facilities, such as the Radioactive Ion Beam Factory (RIBF) at the RIKEN Nishina Center for Accelerator Based Science in Japan, have extended the reach of nuclear physics experiments to isotopes near or at the path of the r-process. This will provide, in the near term, a wealth of new nuclear data essential to improve the reliability of r-process nucleosynthesis models. We present the recent work of the BRIKEN collaboration to measure decay half-lives and beta-delayed neutron emission probabilities of very neutron-rich isotopes at RIBF [1,2]. In particular, we will discuss preliminary results for an experiment in the region of Rh to Cs [3], which are progenitors of the A=130 r-process abundance peak.
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Saturday, April 13, 2019 11:57AM - 12:09PM |
B14.00005: Probing explosive nucleosynthesis via direct nuclear reactions Dennis Muecher, Leyla Atar, Vinzenz Bildstein, Frederic Sarazin, Iris Dillmann, Paul E Garrett, Roman Gernhaeuser, Fabrice Retiere, Artemis Spyrou, Carl E Svensson, Robert Hendersson Detailed information about the heavy, neutron-rich nuclei involved in the r-process are needed in order to pin down the origin of heavy elements in the universe. We have designed an innovative new silicon detector, surrounding an extended gas target, optimized for studies of r-process nuclei. The new $750k TI-STAR silicon tracker detector, under development in an international collaboration at the University of Guelph and TRIUMF, will allow measurements of neutron capture rates in the key A=130 mass region around Sn-132, of pivotal importance for our understanding of r-process nucleosynthesis. TI-STAR also allows unique insight into fission properties of neutron-rich nuclei, important for our understanding of fission re-cycling in the r-process. We present results from S1855 at TRIUMF, targeting resonances with importance for the determination of the neutron flux in explosive nucleosynthesis, to demonstrate the potential of such studies. We also discuss the possibility to couple TI-STAR to GRETINA at FRIB. |
Saturday, April 13, 2019 12:09PM - 12:21PM |
B14.00006: Nucleosynthesis of “light r elements” in neutrino-drive winds. Role of (α,n) reaction rates. Jorge Pereira, Almudena Arcones, Julia Bliss, Fernando Montes The observation of a kilonova (AT 2017gfo) associated with the gravitational-wave source GW170817 in the summer of 2017 provided direct evidence that r-process matter is synthetized in binary neutron-star mergers. Whereas this site is likely the main host for the main r process, responsible for the robustness of the abundance pattern in the region past Z=56, other astrophysical sources might contribute to the production of lighter elements around the 1st peak (e.g. Sr, Y, Zr). Neutrino-driven winds following core-collapse supernovae explosions have been proposed as a possible scenario where the synthesis of the so-called “light r elements” (between Fe and Ag) might occur. Steady-state model calculations, combined with nucleosynthesis reaction networks indicate a substantial sensitivity of the element abundances to (α,n) reaction rates and the astrophysical conditions (e.g. alpha-to-seed and neutron-to-seed ratios). In this presentation, I will summarize the most relevant aspects of our study, emphasizing the (α,n) nuclear reactions that have the most impact in the resulting abundances. Preliminary experimental results on some of these reactions will be briefly discussed |
Saturday, April 13, 2019 12:21PM - 12:33PM |
B14.00007: Understanding r-process and Nuclear Structure via β-delayed Neutron Emission Studies in the 78Ni Region Maninder Singh, Robert Grzywacz, Rin Yokoyama, Thomas T King, Miguel Madurga Flores β-decay studies of nuclei far-off the line of stability and neutron-rich side are crucial in understanding nuclear structure evolution, and provide inputs for r-process [Burdbidge et al., 1957] simulations. Half-lives, one- and two-neutron emission probabilities (Pn, 2n), and neutron energy spectra are the most critical observables, helpful in simulating r-process pathway. The region (26 ≤ Z ≤ 34) around doubly magic 78Ni lies on the r-process pathway and provides a testing ground for the completeness of various physical models. Focus here is on the experiment performed at RI-beam Factory at RIKEN Nishina Center, Japan to study the region by performing time-of-flight based spectroscopy for the delayed neutrons using detector array called VANDLE [W.A. Peters et al., 2016]. Direct measurement of energy spectra will provide information about the Gamow-Teller strength distributions. It will also directly verify the conclusions from the BRIKEN experiment [R. Yokoyama et al., submitted to Phys. Rev. Lett.] where evidence for dominating single neutron emission from 2n unbound states was observed in 84-87Ga decays.
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